1. Field of the Invention
The present invention relates to a synchronizer ring, and more specifically to a synchronizer ring which has a high scuffing resistance, an excellent friction characteristic, and improved abrasion resisting property and durability, and moreover, provides an easy manufacture thereof and is stable in quality.
2. Description of the Related Art
A synchronizer ring has conventionally been utilized, for example, for a synchromesh transmission.
The synchronizer ring acts as a friction ring performing a synchronous sliding motion with a rotating opposite object member such as a taper cone of a clutch gear and a separating motion from the taper cone, thus significantly serving as a member for rendering equal peripheral speeds of two gears which are to be engaged with each other. There has conventionally known a synchronizer ring having a structure as shown in FIG. 1, in which a plurality of gear teeth 100 to be engaged with a rotating object member are formed on an outermost peripheral surface of the synchronizer ring with equally spaced relationship in the circumferential direction thereof, and a plurality of annular grooves 102 are formed on the inner peripheral surface 101 thereof, which is to be brought into contact with the taper cone, for imparting friction force to the inner peripheral surface 101. Longitudinal grooves 103 for escaping lubricant oil may be formed on the inner peripheral surface 101 of the synchronizer ring so as to intersect the annular grooves 102 as an occasion demands. The synchronizer ring is provided on its outer peripheral surface with key grooves 104 to which a synchronizer key is fitted. Such a synchronizer ring is generally made of brass (Cu--Zn alloy).
In general, the synchronizer ring having such a structure is required to have high mechanical strength and accuracy, and moreover the inner peripheral portion thereof which is to be brought into contact with the rotating object member is required to have an excellent friction characteristic as well as sufficient abrasion resisting property and scuffing resistance. Particularly, in the field of a transmission mechanism for automobiles, it has been required for the synchronizer ring to have further improved friction characteristic and abrasion resisting property, since there has been a demand for reliable operability and high grade and sporty-operational feeling of the transmission mechanism for an automobile along with a recent requirement of the transmission mechanism itself with high grade and high performance.
In accordance with such a requirement, various studies have been made for providing a synchronizer ring having an inner peripheral portion having further improved friction characteristic and abrasion resisting property in comparison with the conventional synchronizer ring made of brass (Cu--Zn alloy).
For example, there is known from Japanese Patent Publication No. 46-15043 a synchronizer ring having an inner peripheral portion on which a layer formed of a composite material in which metal, ceramics and oxide are uniformly mixed, is formed through fusion bonding by means of a thermal spraying method. Furthermore, as a method usable for manufacture of the synchronizer ring, there is also known from German Patent No. 3705661 a method for manufacturing a friction ring having an inner peripheral portion on which there is formed by a flame jetting method a friction lining composed of a sintered powdery material including for example metallic powdery component of 80 wt. % and non-metallic powdery component of 20 wt. %.
Furthermore, there has also been studied a synchronizer ring composed of an Fe sintered alloy, a matrix of which comprises bainite and pearlite, and a free Cu phase.
However, the two conventional synchronizer rings described above (i.e., the conventional synchronizer ring having the inner peripheral portion on which the layer formed of the composite material in which metal, ceramics and oxide are uniformly mixed, is formed through fusion bonding by means of the thermal spraying method, and the other conventional synchronizer ring obtained by the application of the method for manufacturing the friction ring having the inner peripheral portion on which there is formed by the flame jetting method the friction lining composed of the sintered powdery material including metallic powdery component of 80 wt. % and non-metallic powdery component of 20 wt. %.) have not as yet been improved to an extent that necessary friction characteristic and abrasion resisting property could be obtained. Further, in the conventional synchronizer rings, there are problems of degradation of strength due to insufficient diffusion of the respective metallic components, and of unstable quality due to unevenness of quality of materials of the flame-coated film. Moreover, incompletely fused particles, or scattering or rebounding particles in the flame may often be entangled in the surface layer of the flame-coated film, and the adhesion of these particles on the surface layer thereof coarsens the surface of the flame-coated film, with the result that the friction characteristic may easily be changed in the lapse of time, abrasion of parts or elements of a transmission system of an automobile may be caused by particles dropped down from the flame-coated film, and scuffing may easily be caused, thus leading to unfavorable problems. In view of these problems, a grind working or a cut working has been applied to the surface of the flame-coated film for the purpose of improving the surface coarseness or roughness of the flame-coated film to make it smooth. Such workings however have disadvantage of much cost required and uneconomical use of raw materials due to ground or cut portions of the flame-coated film.
The above-described synchronizer ring composed of the Fe sintered alloy which comprises the matrix comprising the bainite and the pearlite, and the free Cu phase, has a higher hardness of at least HRB90 since it contains the bainite, thus making it difficult to apply the synchronizer ring to a size working. In addition, coefficient of dynamic friction of the synchronizer ring should further be improved.